1. Field of the Invention
The present invention relates to a composite porous body, a gas diffusion layer member of a polymer electrolyte fuel cell, a cell member for the polymer electrolyte fuel cell, and manufacturing methods thereof.
2. Description of the Related Art
Sheet-like conductive porous bodies having a three-dimensional mesh structure are applied to various kinds of use, such as filters, heat-radiating members, water-absorbing members, and gas diffusion layer members for polymer electrolyte fuel cells and are provided in various apparatuses. However, since these types of conductive porous bodies generally have properties of low-strength and easy deformation, difficulties in handling of the conductive porous bodies such as a difficulty in incorporating the conductive porous bodies into apparatuses have conventionally been indicated. As means for solving this problem, there has been known, for example, a configuration in which a dissimilar material is filled into an end area of a conductive porous body to reinforce the conductive porous body as disclosed in Patent Document 1 (see JP-A No. 48-13956), or a configuration in which a solid such as metal or plastic is filled into fine pores of the conductive porous body to provide holes for fixation to an apparatus to the conductive porous body, thereby providing the conductive porous body with a portion with increased strength, as disclosed in Patent Document 2 (see JP-A No. 08-53723).
Also, the polymer electrolyte fuel cells using the gas diffusion layer members have been paid attention to as domestic stationary power sources, power sources of an electric vehicle, or power sources for small-sized portable equipment. The polymer electrolyte unit cells include a so-called stacked type fuel cell (for example, see Patent Document 3: JP-A No. 08-78028) in which a plurality of unit cells are stacked on each other, as one of structures for sequentially connecting the unit cells.
In recent years, portable, small-sized polymer electrolyte fuel cells have been developed with use of a polymer electrolyte. Generally, since a pair of electrodes (unit cells) in a polymer electrolyte fuel cell causes a small electromotive force, the fuel cell has a structure of a plurality of unit cells being connected in series. Meanwhile, if the stacked type fuel cell is adopted, a separator plate should be disposed between stacked unit cells, and a methanol aqueous solution as fuel or air is required to be fed through stacked narrow fluid channels, which needs an auxiliary mechanism such as a pump. For this reason, this is disadvantageous in volume, weight, cost and the like. Thus, so-called flat fuel cells have now been developed for saving space by arranging unit cells in a plane without using such a separator plate to connect the unit cells to each other.
As the flat fuel cells, for example, the following configuration (for example, see Patent Document 4: JP-A No. 2002-56855) is suggested. That is, according to disclosure in Patent Document 4, unit cells are configured that such an electrolyte layer is interposed between a fuel electrode and an air electrode, connecting plates are disposed on the surfaces of the fuel and air electrodes of each of the unit cells opposite to the electrolyte layer, and the fuel electrodes and the air electrodes of adjacent unit cells are connected sequentially by the connecting plates.
Further, the electrodes (unit cells) of the polymer electrolyte unit cells are manufactured by, for example, basic composite elements having an electrolyte layer, a pair of (two) flat plate-shaped electrodes adjacent to both sides of the electrolyte layer, a sealing portion provided around the electrolyte layer and the electrodes to air-tightly hold the electrolyte layer and the electrodes (for example, see Patent Document 5: JP-A No. 2002-280025).
However, in the configuration described in Patent Documents 1 and 2, a dissimilar material is filled into pores of the conductive porous body, and the pores of the conductive porous body having a three-dimensional mesh structure are then crushed, whereby the crushed portion is used as a reinforcing portion to increase the strength of the conductive porous body. Therefore, the effective use area of the conductive porous body is inevitably reduced. Accordingly, new problems have occurred in that desired functions in the above use of the conductive porous body may deteriorate, or the size of the conductive porous body may be made large for supplementing such a reduced number of pores of the conductive porous body. Also, a dissimilar material, for instance, resin, is filled into the conductive porous body, and this portion is used as a reinforcing portion to increase the strength of the conductive porous body. Thus, if holes for fixation to an apparatus are bored in the reinforcing portion, there is a problem that it is difficult to realize high-precision working, for example, a problem that a cut end of the conductive porous body is exposed to inner peripheral edges of the holes.
In the configuration described in Patent Document 3, the separator plate disposed between the stacked unit cells is provided with grooves for supplying fuel (hydrogen) or air (oxygen) to the gas diffusion layer. In this case, a problem also occurs in that the volume and weight of the separator plate required to have a certain degree of thickness for the grooves hinder that a fuel cell is made small-sized and lightweight.
Moreover, since the conductive porous body, such as a carbon sheet, constituting the gas diffusion layer, has properties of low strength and easy deformation, there is a problem in that its handling is difficult, which may result in a difficulty in manufacturing fuel cells.
In the configuration described in Patent Document 4, a number of processes should be carried out, including, first, forming a plurality of unit cells in which gas seal part, a fuel electrode and an air electrode are integrated into one, then arranging the unit cells at predetermined intervals on a plane, then sequentially disposing Z-shaped connecting plates to be connected to one bottom face and the other top face of each of adjacent unit cells, and filling a sealing agent into a gap between the connecting plates, and the number of members to be assembled is large. Therefore, the manufacture of the flat fuel cell is not easy.
When the fuel cell is intended to be made smaller, it is difficult to surely fill a sealing agent into a minute gap between unit cells having a multi-layered structure. Thus, there is a fear that problems such as poor insulation between the unit cells and leakage of fluid fuel due to insufficient filling of the sealing agent may be caused. Moreover, in the configuration described in Patent Document 4, since the conductive porous body, such as a carbon sheet, constituting the gas diffusion layer, has properties of low strength and easy deformation, there is a problem in that its handling is difficult, which may result in a difficulty in manufacturing fuel cells.
In the configuration described in Patent Document 5, in sequentially connecting a plurality of unit cells, there is a stacked type fuel cell in which the unit cells are stacked on each other, and a separator plate is disposed between adjacent unit cells.
However, when the stacked type fuel cell is constituted with the basic composite elements in which the electrolyte layer and the electrodes are integrated into one, since a gas diffusion layer should be disposed in each electrode for supplying fuel or air (oxygen) to the electrodes and further a separator plate should be disposed between the stacked unit cells, the volume or weight occupied by the separator plate in a whole fuel cell may increase.
Further, since a methanol aqueous solution as fuel or air is required to be fed through the stacked narrow fluid channels and thus an auxiliary mechanism such as a pump is required, this is disadvantageous in volume, weight, cost and the like. Moreover, since a number of the basic composite elements, the gas diffusion layer and the separator plate should be assembled while the sealing performance between these members is ensured, fuel cells of a configuration which can be more easily manufactured with high-productivity are needed.